The studies are aimed at achieving an understanding of the biochemistry, distribution, and function of two neural cell surface molecules. Specific antibodies against these molecules are being used to purify and analyze the molecules, to trace the lineage and fate of cells that express the molecules, and to probe the roles that the molecules play in cell-cell recognition in the developing rat central nervous system. These two molecules define two distinct stages in the development of neural cells: (1) an undifferentiated germinal stage and (2) a very early stage of differentiation immediately following the germinal stage. The D1.1 ganglioside is a derivative of the GD3 ganglioside in which a sialic acid moiety is 0-acylated. D1.1 is present on proliferating cells of the major germinal zones of the rat central nervous system. Studies will be focused on an interaction between D1.1 and fibronectin which may serve to hold dividing cells in germinal zones. The loss of D1.1 from postmitotic cells could allow these cells to begin migration out of proliferative zones. An alternative role for D1.1 as a cell surface receptor for a mitogen will also be examined. These studies will explore the possibility that D1.1 is involved in the regulation or stimulation of cell division. The NG2 proteoglycan is a chondroitin sulfate proteoglycan that first appears on a subpopulation of cells as they emerge from germinal zones and begin to differentiate. The potential of these NG2-positive cells is more restricted than that of D1.1-positive stem cells. They can differentiate into a limited number of cell types, including inhibitory interneurons and fibrous astrocytes. Studies are planned to investigate the factors which control this choice of pathways and to determine whether the choice involves induction or selection of a particular phenotype. Strategies are also presented for cloning the gene for the NG2 core protein. Structural information on NG2 would permit comparison with other types of proteoglycans.